This invention relates to the production of acetyl anhydrides, and optionally of acetic acid, and particularly to a process for the production of such substances from methane and carbon dioxide.
The primary process route used today for production of acetic acid is by catalytic reaction of methanol and carbon monoxide. Such a process, typically termed “carbonylation”, is described in a number of patents and publications. Rhodium, palladium or iridium-containing catalysts have been found especially useful for conducting this reaction. A recent example of a patent on such a process is U.S. Pat. No. 6,472,558 of Key et al., which describes a process for reaction of methanol (and/or a reactive derivative of methanol such as methyl acetate or dimethyl ether) and carbon monoxide in a liquid reaction composition that comprises methyl acetate, methyl iodide, acetic acid, water and a polydentate phosphine oxide, in addition to the iridium catalyst.
Another process route that has been found useful for the production of acetic acid involves the catalytic oxidation of ethane. Such processes are disclosed, for instance, in U.S. Pat. No. 6,383,977 of Karim et al. and U.S. Pat. No. 6,399,816 of Borchert et al. In the processes described in both patents, a mixed oxide catalyst containing multiple metals is used. Karim et al. discloses catalysts containing molybdenum, vanadium, niobium and palladium, while Borchert et al. discloses containing molybdenum and palladium, plus preferably vanadium, niobium, antimony, nickel and calcium.
Methane is the lowest molecular weight, and simplest in structure, of the hydrocarbons. Because of the existence of large reserves of methane worldwide it has been considered desirable for some time to develop processes to convert methane to more valuable chemicals. Processes for production of acetic acid from methanol represent an ultimate use of methane, but in current commercial practice, the methane first must be converted to methanol. A process that produces acetic acid directly from methane would be more desirable.
A small amount of work has been conducted so far on the direct conversion of methane to acetic acid, for instance by reaction of methane with carbon dioxide. A process for production of acetic acid by such a reaction was disclosed in the 1924 British patent 226,248 of Dreyfus. The patent describes a process involving gas phase reaction of methane with carbon monoxide and/or carbon dioxide in the presence of a catalyst that preferably contains nickel carbonate. Apparently a mixture of acetic acid, acetaldehyde and possibly acetone is obtained. No data on yields or conversions is contained in this patent.
PCT application WO 96/05163 of Hoechst A. G. describes a gas phase reaction of methane and carbon dioxide to produce acetic acid, using a catalyst containing one or more Group VIA, VIIA and/or VIIIA metals. Selectivities of 70-95% based on methane are asserted; however the application contains no exemplary data.
A number of researchers have investigated production of acetic acid by liquid phase carbonylation of methane with carbon monoxide, due to the favorable thermodynamics of this reaction. See, for instance, Bagno, et al. J. Org. Chem. 1990, 55, 4284-4289; Lin, et al., Nature 1994, 368, 613-615, Chaepaikin, et al., J. Mol. Catal. A: Chem. 2001, 169, 89-98; Nishiguchi, et al., Chem. Lett. 1992, 1141-1142; Nakata, et al. J. Organomet. Chem. 1994, 473, 329-334; Kurioka, et al., Chem. Lett. 1995, 244; Fujiwara, et al., Studies in Surface Science and Catalysis 1998, 119, 349-353; Taniguchi, et al., Org. Lett. 1999, 1(4), 557-559; Asadullah, et al., Tetrahedron Lett. 1999, 40, 8867-8871; and Asadullah, et al., Chem. Int. Ed. 2000, 39(14), 2475-2478.
Kurioka et al. (1995, supra) also reported a liquid phase experiment in which methane was reacted with carbon dioxide in the presence of palladium acetate, cupric acetate, potassium persulfate and trifluoroacetic acid, reportedly producing acetic acid. The yield was said to have been 1650% (based on the palladium). This work was continued and further reported on by Taniguchi et al., Studies in Surface Science and Catalysis 1998, 439-442. That publication described a series of experiments in which methane and carbon dioxide were reacted in the presence of catalysts, primarily vanadium-containing catalysts such as vanadium(acac)2 [acac=acetylacetonate], sodium metavanadate, and vanadium pentoxide, and in the presence of liquids including pure trifluoroacetic acid (“TFA”) and aqueous solutions of TFA, hydrochloric acid, sulfuric acid, and sodium hydroxide, as well as simply in water. The best results were obtained in a system that contained only TFA; the worst results were with water alone.
Taniguchi et al. (1998) hypothesized that the acetic acid was produced by reaction of methane and carbon dioxide, but subsequent work by others (and by us) showed that this was not correct; in the Taniguchi et al. work the acetic acid would have been produced primarily if not entirely by reaction of methane and TFA, with concomitant production of one mole of fluoroform for each mole of acetic acid produced by this reaction. TFA, however, is an expensive feedstock for the production of acetic acid. In addition, it is difficult to reconvert the fluoroform byproduct to TFA for recycle or reuse.
Nizova et al., Chem. Commun. 1998, 1885 reported results of reactions of methane with carbon monoxide in aqueous systems to produce acetic acid. The authors mention that they had also produced acetic acid by reaction of methane and carbon dioxide in an aqueous system, in the presence of a sodium metavanadate/pyrazine-2-carboxylic acid catalyst. However, the yield (based on methane) appears to have been quite low and pressures rather high (50 bar). Piao et al., J. Organomet. Chem. 1999, 574, 116-120 and Yin et al., Appl. Organomet. Chem. 2000, 14, 438-442 reported on catalytic partial oxidation of methane to methyl trifluoroacetate, in the presence of trifluoroacetic acid and a small amount of trifluoroacetic acid anhydride, but with no CO or CO2 present. More recently, Reis et al., Angew. Chem. Int. Ed. 2003, 42, 821 described production of acetic acid from methane in a single-pot reaction, with trifluoroacetic acid and various vanadium-containing catalysts, notably amavadine, Ca[V[ON(CH(CH3)COO)2)2], but in the absence of carbon dioxide.
It would be desirable to provide a process for production of acetic acid more directly from methane, and particularly from a process that involves methane and carbon dioxide rather than carbon monoxide since carbon dioxide is relatively cheap, and additional oxygen is not needed. A process conducted under relatively mild conditions, adaptable to industrial use rather than a laboratory curiosity, and with good conversions and/or yields, would be highly desirable.
An improved process for the production of acetyl anhydrides also would be desirable. An acetyl anhydride compound can be defined as a compound, which upon reaction with water liberates acetic acid and another non-hydrohalogenoic acid. Alternatively an acetyl anhydride compound may be described as a compound in which the hydroxy group of acetic acid has been replaced with the anion of a non-hydrohalogenoic acid. Acetyl sulfate is one example of an acetyl anhydride. It typically is produced by reacting acetic anhydride with sulfuric acid and has a number of uses, for instance as a sulfonating agent and as a chemical intermediate.